SES kits are designed to keep the vehicle level at all times and prevent roll and sway. The Aeon rubber springs found in a Timbren SES kit have a progressive spring rate. In other words, you are guaranteed a soft, comfortable ride at all times. This SES Suspension Upgrade fits the rear suspension of a Compatible With Chevrolet Silverado 2500/3500 & Compatible With GMC Sierra 2500/3500 truck. We’ve engineered our hollow rubber springs to deliver a progressive spring rate. In other words, the more weight that pushes down on the rubber springs the harder they work to prevent rear end sag. Whether you’re pulling a trailer or carrying a heavy load in the bed of your truck, our hollow rubber springs adjust automatically to keep the vehicle level at all times. This SES Suspension Upgrade replaces the jounce stop on the frame. Its unique design ensures superb ride quality – loaded or unloaded. (There should be a ½” to 1 ½” gap between rubber spring and axle to ensure unloaded ride quality.) Unlike other auxiliary spring systems, the SES Suspension Upgrade guarantees the best of both worldsTimbren Suspension Kits (SES Kits) are designed to enhance the suspension of your vehicle. Easiest to use: Rubber cushions absorb road shocks and automatically adjust to uneven loads or road conditions. Easiest to maintain: There are no airlines or fittings to allow leaks. Simply bolt the kit on and you are set for a lifetime of trouble free suspension. Easiest to install: There are no holes to drill, no airlines to route and SES Kits can be installed in a matter of minutes using basic hand tools. The softer ride quality of todays trucks and the mediocre suspensions found on most trailers can cause excessive trailer sway, instability and suspension settling. Timbrens high performance suspension packages will ensure added safety and peace of mind.